GIFT   OF 


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UN  I  VERSITY^F~  CALIFORNIA 
COLLEGE  OF  AGRICULTURE 

BERKELEY,   CALIFORNIA 


AGRICULTURAL  EXPERIMENT  STATION 
THOMAS   FORSYTH   HUNT,  DIRECTOR 


CIRCULAR  No.  82 

(NOVEMBER,  1912.) 


THE   COMMON   GROUND   SQUIRRELS   O 

H.  C.  BRYANT. 

Two  rodents  in  the  State  of  California  give  the  rancher  more  trouble 
than  all  the  other  animal  pests  combined,  insects  excepted.  One,  the 
pocket  gopher  (Thomomys  sp.),  feeds  largely  on  the  roots  of  plants  and 
trees  and  hence  is  one  of  the  worst  pests  of  the  garden  and  orchard. 
The  other,  the  ground  squirrel  (Citellus  sp.,  Ammospermophilus  sp., 
Gdllospermopkilus  sp.)  is  especially  destructive  to  grain,  but  it  is  also 
destructive  to  nuts  and  fruit.  The  established  fact  that  the  California 
ground  squirrel  is  instrumental  in  spreading  bubonic  plague  has  made 
these  animals  of  more  than  ordinary  economic  importance. 

These  two  principal  rodent  pests  are  easily  distinguished  by  their 
general  appearance,  size,  habits,  and  burrows.  The  pocket  gophers  have 
very  short  ears,  small  eyes,  short  tails,  and  cheek  pouches  which  open 
externally  ;  they  are  relatively  small  (6  to  10  inches),  largely  nocturnal, 
and  live  almost  entirely  in  their  burrows.  Ground  squirrels  have  rela- 
tively large  ears  and  eyes,  longer  tails,  and  the  cheek  pouches  do  not 
open  externally  ;  most  of  them  are  larger  in  size,  diurnal,  and  forage  for 
food  above  ground.  The  burrow  of  the  pocket  gopher  can  be  distin- 
guished by  a  mound  of  earth  surrounding  the  entrance,  and  by  the  fact 
that  the  opening  is  nearly  always  kept  plugged  full  of  earth.  The 
burrow  of  the  ground  squirrel  on  the  other  hand  is  usually  open,  with 
the  excavated  earth  thrown  out  on  one  side  of  the  entrance  only.  One 
or  more  runways  lead  away  from  the  burrow. 

According  to  Merriam,1  the  ground  squirrels  of  California  may  be 
arranged  in  four  groups:  (a)  the  large,  long-eared  gray  ground  squirrel 
(subgenus  Otospermophilus)  •  (b)  the  small,  short-eared,  brownish 
species  (genus  Citellus)  ;  (c)  the  small,  white-striped,  antelope  ground 
squirrel  of  the  deserts  (genus  Ammospermophilus)  •  (d)  the  golden- 
mantled  ground  squirrel  of  the  mountains  (genus  Callospcrmophilus). 

The  "digger"  ground  squirrels  (Citellus  sp.),  which  belong  to  the 
siibuvnus  Otospermophilus,  are  not  only  the  most  destructive,  but  are 
the  disease  carriers  (Fig.  1).  These  ground  squirrels  usually  live  in 
colonies,  their  burrows  often  being  connected  for  a  considerable  dis- 
tance. Food  in  the  shape  of  grain,  seeds,  and  fruit  is  stored  for  the 
winter  season.  The  call  note  is  a  single  loud  whistle.  The  warning 
note  is  a  similar  short  whistle  followed  by  two  or  three  chattering  trills. 
Young,  numbering  from  five  to  ten,  are  usually  born  in  March  and 
April.  This  ground  squirrel  has  been  found  infected  with  bubonic 
plague,  and  several  cases  of  human  plague  have  been  traced  to  a  bite 


riam.    r. 
no.    52.   pp.    1-8. 


Hart. 


California    Ground    Squirrels.     Treas.    Dept.,    Public    Health    Reports,    rol.    23, 


294980 


of  one  of  these  animals.  The  real  danger  of  the  spread  of  infection 
lies  in  the  dissemination  of  infected  fleas.  As  has  been  shown  by  the 
recent  campaign  against  these  ground  squirrels,  carried  on  by  the  U.  S. 
Public  Health  and  Marine  Hospital  Service,  eradication  of  this  pest 
depends  largely  on  persistent  work  of  the  individual. 

This  group  of  long-eared  gray  ground  squirrels  has  a  wide  range, 
being  found  throughout  the  State.  Several  species  and  several  varieties 
of  each  have  been  recognized.  Each  variety  or  subspecies  occupies  a 
fairly  well-defined  region  of  the  State,  so  that  they  can  usually  be  dis- 
tinguished by  the  locality  in  which  they  are  found.  The  northern  coast 
form  is  known  as  the  Douglas  ground  squirrel  (Citellus  douglasi)  • 
that  of  the  interior  valleys,  as  the  California  ground  squirrel  (Citellus 


FIG.  1. — Two  varieties  of  the  common  "digger"  ground  squirrel  of  California,  found 
throughout  the  State.  The  squirrel  above  is  the  Douglas  ground  squirrel  (Citellus 
douglasi),  found  along  the  coast  north  of  San  Francisco  Bay;  the  one  below  is  the 
California  ground  squirrel  (Citellus  beecheyi  beecheyi),  the  common  ground  squirrel 
of  the  interior  valleys  and  the  carrier  of  bubonic  plague. 

beeckeyi  beecheyi)  ;  and  that  of  southern  California,   as  the  Fisher 
ground  squirrel  (Citellus  beecheyi  fisheri) . 

In  the  extreme  northeastern  corner  of  the  State  and  to  some  extent 
in  the  northern  part,  a  smaller  brown  ground  squirrel  is  found  in 
abundance.  It  is  known  as  the  Oregon  ground  squirrel  (Citellus 
oregonus) .  The  ground  squirrel  of  the  desert  is  much  smaller  than  the 
common  "digger"  squirrel  and  is  striped.  It  is  called  the  desert  or 
round-tailed  ground  squirrel  (Citellus  tereticaudus) .  A  small  striped 
form  belonging  to  another  genus  (Ammospermophilus)  is  found  to  a 
limited  extent  in  the  San  Joaquin  Valley,  and  a  variety  of  the  same 
species  in  the  rocky  places  in  the  deserts  and  foothills  bordering  the 
deserts.  These  forms  are  known  as  the  Nelson  ground  squirrel  and  the 
Antelope  ground  squirrel.  Neither  are  abundant  enough  to  be  of  great 
economic  importance.  Golden-mantled  ground  squirrels  (Callospermo- 
philus  sp.),  more  often  called  red-headed  chipmunks,  are  mountain 
species  and  seldom  give  trouble  (Fig.  2). 


CONTROL  OF  GROUND  SQUIRRELS. 

H.    J.    QUAYLE. 

There  an-  two  methods  of  destroying  ground  squirrels:  first,  by  means 
of  poisoned  grain,  and,  second,  by  the  liberation  of  carbon  bisulfid 
in  their  burrow.s.  Which  of  the  methods  to  be  followed  will  depend 
upon  tin-  season,  th<- •poison  .irrain  im-tlmd  brin«r  more  effective  during 
the  dry  season,  while  the  carbon  bisulfid  treatment  will  be  more  effective 
during  the  rainy  season  when  there  is  sufficient  soil  moisture  to  prevent 
the  ircnenil  diffusion  of  tin-  iras  In-yond  the  open  burrows. 


FIG. 2. — Arranged  from  left  to  right  are  the  ground  squirrels  of  less  economic 
importance  in  California,  the  Oregon  ground  squirrel  (Citellus  oregonus),  golden- 
mantled  ground  squirrel  (Callosppriiiovhiius  chr ysodeirus ) ,  Antelope  ground  squirrel 
(AmmoBpermophiliu  Irucurus),  and  the  desert,  or  round-tailed  ground  squirrel 
(Citellus  tereticaudus) . 

Where  ground  squirrels  are  abundant  over  considerable  areas,  the 
simplest,  most  effective  and  least  expensive  way  to  destroy  them  is  by 
the  use  of  poisoned  orrain.^  Barley  is  the  grain  to  be  preferred,  since  it 
is  more  attractive  v  tae  squirrels  and  less  likely  to  be  eaten  by  birds. 

The  formula  and  method  of  preparation  are  as  follows : 

<  'l-'jiti  barley 20    quarts. 

Strychnia  sulphate    ( ground  or  powdered  I 1    ounce. 

Saccharine 1    teaspoonful. 

Gloss  starch   (or'dinary  laundry  starch) \  teacupful. 

W;r  1*  pints. 


Dissolve  the  starch  in  a  little  cold  water  and  add  1J  pints  of  boiling 
water,  making  a  rather  thick  solution.  While  hot,  stir  in  the  strych- 
nine and  mix  until  free  from  lumps ;  then  add  the  saccharine  and  beat 
thoroughly.  Pour  in  the  poisoned  starch  over  the  barley  and  stir 
rapidly  until  the  poison  is  evenly  distributed;  then  allow  the  grain  to 
dry.  When  dry  it  will  keep  indefinitely  without^  deterioration. 

By  this  method  a  coating  of  poison  is  formed  on  the  outside  of  the 
grain,  which  acts  much  more  quickly  than  if  the  grain  is  boiled  or 
soaked  in  the  poison.  Squirrels  are  also  readily  killed  by  carrying  such 
coated  grain  in  their  cheek  pouches  while  storing  food  for  future  use. 

PUTTING    OUT    THE     POISON. 

The  poisoned  grain  should  be  scattered  (not  placed  in  heaps)  on  clean 
hard  places  about  the  colonies,  the  trails  between  the  holes,  along  fences 
and  roadsides  and  other  places  frequented  by  the  squirrels.  The  time 
to  apply  it  is  during  the  dry  season.  If  distributed  just  at  the  end  of 
rainy  season,  late  March  or  early  April,  it  will  destroy  them  during  the 
breeding  period,  when  one  killed  is  equivalent  to  eight  or  nine  later  in 
the  season.  The  poisoning  may  continue,  however,  throughout  the  sum- 
mer and  early  fall.  This  poisoned  grain  as  it  is  scattered  about  is  not 
dangerous  to  stock,  but  is  fatal  to  poultry. 

COST. 

The  cost  of  preparing  the  material  according  to  the  formula  given 
varies  from  about  $4.00  to  $4.75  per  100  pounds.  One  hundred  pounds 
of  the  poiscned  barley  is  sufficient  to  treat  200  or  300  acres.  It  may  be 
distributed  from  horseback. 

CARBON    BISULFID. 

A  tablespoonful  of  crude  carbon  bisulfid  is  poured  over  a  small  ball 
of  cotton  waste,  corn  cob  or  other  absorptive  material  and  placed  as 
far  down  the  burrow  as  possible,  and  the  hole  is  tamped  in. 

It  is  used  to  best  advantage  when  the  soil  is  wet.  In  wet  soil  the 
interspaces  are  filled  with  water  and  thus  general  diffusion  of  the  gas 
through  the  soil  is  prevented. 

Carbon  bisulfid  is  a  volatile  liquid  and  rapidly  loses  its  strength 
on  exposure  to  air.  It  should  therefore  be  kept  in  tight  containers.  It 
is  also  inflammable  and  explosive.  It  should  be  used  only  in  burrows 
known  to  be  inhabited  by  squirrels.  The  cost  of  crude  carbon  bisulfid 
is  about  8  cents  per  pound  in  50-pound  carboys  or  drums. 

The  two  methods  described,  poisoning  and  the  carbon  bisulfid  treat- 
ment, may  well  supplement  one  another.  Where  the  area  is  extensive 
the  poison  may  first  be  used,  because  of  its  cheapness,  and  this  followed 
in  the  proper  seas'on  with  the. carbon  bisuLfid  to  clean  up  those  that 
escape  the  poison.  •  **%*JMJk 

Small  areas  may  be  freed  from  squirrels,  but  these  are  likely  to  be 
quickly  reinvested  again  from  tlie  neighboring  territory.  It  is  often 
important,  therefore,  for  the  people  of  a  district  t6v unite  in  a  coopera- 
tive campaign  and  free  large  areas  from  the  squirrel  pest. 


DUASTAMP|DBfcLOW 


UNIVERSITY  OF  CALIFORNIA 
FORM  NO.  006.  «m.  3/80          BERKELEY.  CA  947. 


